The Mythbusters detonated one using incendiary bullets. The explosion was not that large but the flames were substantial. My initial thoughts would be equivalent to a frag grenade plus a double or triple radius Malatov cocktail.
Here is the video. The explosion is about 2 min in
http://www.youtube.com/watch?v=20ZLefQC_oU
edit.
In the US they are very common. Gas stations, convenience, hardware and grocery stores all may sell them.